Radiation interrupters



c. WTMUNDAY" I RADIATION INTERRUPTERS April 28, 1959 2 Sheets-Sheet 1 Filed Aug. 25, 1953 INVENTOR.

' CHARL E5 mLTEEML/NDAX YWMMQM ATTORNEYS.

April28, 1959 c. w MUNDAY.J 2,884,543

7 RADIATION INTERRUPTERS 7 Filed Aug. 25. 195: v 2 Sheds-Sheet 2 I uvwsivrox C HARL Es WILTE/PMUND/JX W M8 M ATTUR/VEKS.

RADIATION INTERRUPTERS Charles Walter Monday, New'Eltham, London, England, assignor to The Distillers Company Limited, Edinburgh Scotland, a British company 1 Application August 25, 1953, Serial No. 376,503 Claims priority, application Great Britain August 30, 1952 4 Claims. (Cl. 250-219) The present invention relates to a device for interrupting beams of light and other radiation.

Devices for this purpose are well known in the art and may comprise, for instance, an oscillating shutter or a rotating vane or a perforated rotatable drum. The use of these and other types of light interrupting or chopping means is not completely free from disadvantages. For example in the design of a double beam chopped radiation analyser, where it is desired to chop the two beams of radiation 180 out of phase, it is normally desirable that a given percentage increase of flux in' one ibeam should be accompanied by the same percentage decrease of flux in the other beam. It has not been possible to achieve this with the previously used chopping means (see Analytical Chemist, 1951, volume 23, page 5).' Furthermore, the previously employed chopping means introduced a change-over signal of double the frequency of the chopping means.

The radiation chopping means according to the present invention makes it possible, within mechanical limits,- to eliminate changeover-signal, and also to utilise the maximum aperture of a collimating mirror, if employed, and if desired to divide beams without employing a multiplicity of reflecting surfaces.

Accordingly, the present invention is for radiation chopping means which comprises an endless perforated belt adapted to revolve and to be introduced into the radiation to be interrupted. The present invention is also for a radiation analyser comprising a source providing a .beam of radiation, analysis cells and filter cells mounted in said beam of radiation and a radiation chopping means comprising an endless perforated belt and means for causing said belt to move through said beam of radiation. The endless perforated belt may be introduced into the path of the beam of radiation one or more times as is-desired. Where the said belt interrupts the beam of radiation more than once, it is essentialgthat the belt is carefully aligned in order that the desired interruption of the beam of radiation may be achieved. The plane of the portion of the endless perforated belt interrupting the radiation beam should preferably be at right angles to the plane of said beam.

It is desirable that the endless perforated belt should be of a width at least equivalent to the width of the beam of radiation to be interrupted. The form and distribution of the perforations in said belt will be dictated by the particular nature of the interruption which it is desired to achieve. The perforations are most suitably square or rectangular, as in this way maximum energy of the beam may be utilised and change-over signal may be more simply obviated. The belt is suitably supported by at least 3, and preferably 4 spindles.

Thus for example, if it is desired to divide a beam of radiation into two discrete beams, and interrupt the divided beams alternately without change-over signal, this is suitably efiected by using an endless perforated belt arranged to pass once through said beam of radiation, the perforations of said belt comprising two series of equal square or rectangular perforations disposed side by side, each perforation of each series being separated by a distance equal to the length of the perforation, the perforations of the two series being in a staggered relationship so that the plane of the lower edge of a perforation in one series corresponds to the plane of the upper edge of a perforation in the other series.

The radiation chopping means is of particular application in radiation gas analysers, such for example as are described in J. Optical Society of America, February 1950, pages 112-118, and in my copending United States application Serial No. 117,890, filed August 5, 1950. Such radiation analysers comprise in essence a source providing a beam of radiation, analysis cells, filter cells, radiation chopping means and means for directing the beam onto a radiation detector.

In such radiation analysers the radiation chopping means is very advantageously the radiation chopping means according to the present invention. In these analysers the use of the radiation chopping means according to the present invention makes it possible, within mechanical limits, to eliminate change-over signal, and also to utilise the maximum aperture of the collimating mirrors, where employed and to divide the beam without employing a multiplicity of reflecting surfaces.

With the double beam gas analysers it is suitable to use a phase sensitive detection system and for this purpose a reference voltage whose phase is in a deter-- mined relationship to the phase of the interrupted beams,

and'which is of the same frequency as the said beams;

is required. This may be achieved by an additional. series of perforations provided in the endless perforated belt, adapted to interrupt a beam of light from a lamp. and photocell unit. Adjustment of the phase difference between the reference and interrupted beams is readily obtained by motion of the lamp and photocell unit in a longitudinal direction with respect to the series of perforations.

The invention accordingly comprises the novel apparatus and combinations thereof, specific embodiments of which are described herein by way of example only and in accordance with the manner in which I now pre fer to practice the invention.

The invention will be better understood by referring to the following detailed description of the invention mild ltlo the drawings forming part of this application, in w 1c Figure l is an end elevational view of a radiation chop- Figure 2 is a cross-sectional view of a radiation chop-L ping means as in Figure 1.

Figure 3 is an end elevation view of another radiation chopping means for dividing a beam of radiation and alternately interrupting the two beams formed.

Figure 4 is a diagrammatic side elevational view of an infra-red gas analyser.

Figure 5 is a cut-away top view of the analyser of Figure 4.

In Figures 1 and 2 the radiation chopping means comprises the endless belt 1 supported by spindles 2, and driven by one or more of said spindles as shown by driving means 18. The belt 1 is provided with two series of perforations 3 disposed in staggered relation as shown. In Figure 3 the radiation chopping means comprises the endless belt 4 provided with two series of perforations 5 disposed in staggered relation as in Figure 1. The belt 4 is also provided with an additional series of perforations 6 which may be used to interrupt an independent beam of light to be received by a photo-cell thereby providing a assasas reference phase voltage. Thebelt 4 is also provided with a series of perforations 7 disposed at the edge of the belt, which are adapted'to engage with cog or similar means arranged on the spindles which carry the said belt.

Figures 4 and show diagrammatic views of a double beam infra-red gas analyser. A radiation source 8 is collimated by concave'mirror 9 to give a beam of radiation 10. The beam of radiationpasses through an absorption cell 11, a filter cell 12, is split and interrupted by radiation chopping means 13 of the type shown in Figure 3 employing perforations 19, one split beam passing through analysis cell 14, and the other split beam passthrough analysis cell 15, and the two split beams being concentrated by concave mirror 16 on to the radiation detector 17.

The spindles 20 carrying the chopping means 13 are in the form of cog-wheels as shown which engage with a series of perforations 21 in said chopping means, at least one of said cog-wheels 21 being driven by means 22. A light source 23 provides an independent beam of light 24, interrupted by the further series of perforations 25 provided in said chopping means, is received by photocell unit 26 mounted on an adjustable support 27, thereby providing a reference phase voltage.

In this double beam radiation gas analyser changeover signal can be eliminated, the maximum aperture of the collimating mirror may be utilised and the beams are divided without the use of reflectors.

The position of the belt interrupting the beam of radia tion with respect to the analysis cells, filter cells and ab sorption cells in said apparatus is non-critical, providing the belt interrupts the collimated beam, and the plane of the belt is at right angles to the plane of the collimated beam.

Although the radiation chopping means of the present invention has been described with particular reference to double beam infra-red gas analysers, the radiation chopping means may be usedwith advantage in other radiation analysers. V

The belt comprising the radiation chopping means of the present invention may be constructed of any suitable material opaque to the radiation employed such as thin spring steel, metallised film strips, plastic materials and the like capable of bearing perforations and being rotated over spindles.

I claim:

1. A radiation analyser comprising a source providing a beam of radiation, analysis cells and filter cells mounted in said beam of radiation, a radiation chopping means comprising an endless belt, having a plurality of perforations therein, means for supporting said belt so that the belt'passes once through said beam of radiation, the plane of the belt being at right angles to the beam of radiation, the perforations of said belt comprising two rectilineal series of equal rectangular perforations disposed parallel to one another, each perforation of each series being separated by a distance equal to the length of the perforation, the perforations of'the two series'being in staggered relationshipvso that the plane of .the lower edge of each perforation in one series corresponds to the plane of the upper edge of a perforation in the other series and the plane of the lower edge of each perforation in said other series corresponds to the plane of the upper edge of a perforation in said one series, means for driving said belt, and means for directing the beam onto a radiation detector.

2. A radiation analyser'as in claim 1 wherein the belt is provided with .a further series of perforations and wherein the means for supporting said endless perforated belt comprise spindles provided with cogs which mate with said further series of perforations, the means for driving said belt being connected to at least one of said spindles.

3. A radiation analyser as in claim 1 wherein said belt is provided with a further series of perforations and further comprising means for providing a further beam of light on one side of said belt and directed through said further series of perforations and light responsive means mounted on the opposite side of said belt and in the path of said further beam.

4. A radiation analyser comprising a source providing a beam of radiation, analysis cells and filter cells mounted in said beam of radiation, a radiation chopping means comprising an endless belt having a plurality of rectangular perforations therein, means for supporting said belt so that said belt passes once through said beam of radiation, the plane of the belt being at right angles to the beam of radiation, the perforations of said belt forming two rectilineal series of perforations disposed parallel to one another and the perforations of one series being staggered with respect to the perforations of the-other series in thedirection of movement of said belt so that the plane of the lower edge of each perforation; of one series corresponds to the plane of, the upper edge of a perforation in the other series and the plane of the lower edge of each perforation of said other series corresponds to the plane of the upper edge of a perforation in said one series, means for driving said belt and means for directing the beam onto a radiation detector.

References Cited in the file of this patent UNITED STATES PATENTS 1,319,698 De Brayer Oct. 28, 1919 1,414,942 Gill May 2, 1922 1,996,233 Darrah Apr. 2, 1935 2,339,204 Stockbarger et al. Jan. 11, 1944 2,442,910 Thomson June 8, 1948 2,482,039 Thompson Sept. 13, 1949 2,555,327 Elliott June 5, 1951 FOREIGN PATENTS 354,371 Germany June 8, 1922 1,034,590 France Apr. 15, 1953 

